The yellow truck that gets stuck turning only needs to be redirected and then the rest of the vehicles will turn no problem. Maybe need to delete the yellow truck completely before it reaches intersection?
Well I think(not sure) the game randomly spawns vehicles along the spawn point. So technically its not possible, if this theory is correct, to simply remove the truck like so.
I plan to move the path slightly further into the intersection and see if that will fix it.
The biggest traffic problem i have seen aside from the yellow truck, is at the main intersection where the 2 four lane roads meet. The cars in the right lane(if headed south) try to turn left across the right hand lane and thus traffic gets stuck.
I also found a bug in the chase command. It only works to some extent on the black undercover car. The car will follow the suspect but the officers will not stop the car and draw there guns on the suspect. I tried it with 2 officers in the car and it still didnt work.